/Engine/Source/Runtime/Slate/Public/Framework/Docking/TabManager.h
Activate the NewActiveTab. If NewActiveTab is NULL, the active tab is cleared.
void SetActiveTab ( const [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [SDockTab](API\Runtime\Slate\Widgets\Docking\SDockTab) > & NewActiveTab )